NMR spectroscopy is currently being used at the NIA to study the phosphorous metabolism of peripheral muscle in human volunteers. Age- related and exercise-related changes in the 31P NMR spectrum are under investigation. Studies are performed on subjects of all ages from the BLSA. Further work will focus on organ physiology in animals. One study focuses on 31P metabolism of isolated hearts and will investigate long-term physiologic interventions and their interactions with acute demand and supply stressors. An additional study has been initiated in studies of the isolated perfused lung. Studies of kinetic processes will be performed using magnetization transfer techniques, which provide further insight into the detailed regulation of phosphorous metabolism. In addition, methodolgic studies have been undertaken to further develop the magnetization transfer technique itself, as well as to apply it to problems of intracellular compartmentation.